String galvanometer



Aug. 9, '1938. E. GERLACH 2,126,252

STRING GALVANOMETER Filed Aug. e, 1955 nventor Erwin Gerlach Gttorneg Patented Aug. 9, 193sf Erwin Gerlach, Berlinassignor to Klangfilm Siemensstadt, Germany, G. m. b. H., Berli Germany, a. corporation of Germany Applicationl August 6, jIn G 1935, Serial No. 34,930

ermany October 5, 1934 a claims. `(or 1in-e5)vyThis invention relates to the recording of sound and has for its principal object the provision of l an improved apparatus whereby the zero line of the sound track is shifted for the purpose of obviating or minimizing background noise.

It is customary to produce variable area or variable density sound 'records by means of electrodynamic sound recording apparatus designed to minimize background noise. Such apparatus includes a conductor to which-'is supplied both an audio current whih varies in accordance with the sound to be recorded and a rectified audio current component which varies as the intensity or volume of such sound.

This arrangement is disadvantageous because the direct or rectified current tends to raise the thermal load or stress of the electrodynamic system and for the reason that the resistance of the electrodynarnic system is extremely low and the current required to cause a shift in the zero line corresponds only to a small fall of potential across the terminals of the electrodynamic system. rl'his is undesirable on the ground that the D. C. must be obtained from the microphone currents by way of amplification and rectification, and that the tubes used inconnection therewith present always an internal resistance which is high `in contrast with the resistance of the electrodynamic system. Q'I'he result is that the D. C. energy virl major part is consumed in the last tube and becomes utilizable only in minor part in the electrodynamic system.' For the A. C. power which is supplied to the electrodynamic system, the conditions are more favorable in that the insertion of a transformer between the last amplifier tube for the voice alternating voltage and the sound recorder device arrangements may be madel so that the said last tube furnishes a comparatively high voltageA and a correspondingly low current.

In accordance with this invention this difficulty is minimized by the provision of an improved recording apparatus so constructed that the median position of vibration of the electron dynamic system energized in accordance with the sound to be recorded is varied by means of an electromagnetic system with response to the volume of the sound. i

The invention will be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

The single figure of the drawing is a diagram- 55 matic showing of a sound recording oscillograph y engaged over a tiny .hook i tion of the mirror it.

constructed in accordance with the invention, certain elements being omitted to simplify the drawing.

In the exemplified embodiment of the invention, it denotes the current-traversed wire or 5 ribbon of the electrodynamic system to which is attached a mirror Il. A magnetic field is pro- -vided by the magnet 2l. The wire lli is attached to the insulation member i2 and is connected at its opposite ends to the terminals it and it. lo At the left-hand or looped end of the wire it where it presents a bend of 180 degrees there is the wire it of a ferromagnetic system The left-hand end of the Wire it is firmly tensioned at point lll. Approxl5 imately'in the middle of the wire it isthe ferromagnetic body or magnetic core it. The latter projects into the interior of a coil it which is placed in a'plane parallel to the plane of the mirror Ill. Between the body it and the hook it is a cross piece it. In a manner similar to that disclosed by Robinson Patent 1,854,159, the rectified part of the signal is applied to'the coil 20 and functions to twist the loop it so that the peaks of the low t and high amplitude oscillations are maintained more nearly in alignment with one another than would be the case if vibration of the loop were not thus controlled by the coil 2t. As applied to the recording of impulses, this has4 the ad- 30 vantage that the zero reference line of the impulses is shifted from the edge of the record only to the extent required to prevent overshooting the edge of the record.

In the operation of the apparatus the terminals it and it are fed with the audio current corresponding to the sound with the result that the mirror ii undergoes oscillations at the rate and vrhythm of the sound. The center of oscillations of the mirror is displaced by means of the coil which surrounds the ferromagnetic body it and is supplied with direct current obtained by rectification of part of the audio current. The magnetic core it will then occupy and assume positions inside the coil which will change in accordance with the momentary size of this D. C. and thereby will alter the median position of oscilla- IVlhe core it is not subjected to audio frequency vibrations for the reason that the entire arrangement is immersed in oil. The wire Il' slids over the edge of the crosspiece l@ as the body it is displaced.

It will be .apparent that this arrangement is useful both for records made by the variable density method and the variable area or multi-peak method.

I claim:

l. A galvanometer including means movable in accordance with vibrations to be measured, a. support for said means, and means operable to shift the position of said support in accordance with a rectied component of said vibrations.

2. A gaivanometer including a looped conductor adapted to receive current corresponding to vibrations to be measured, a reflector mounted on said conductor, conductor supporting means,

and electromagnetic means energized in accord' ance with the amplitude of said vibrations forv changing the position of said support.

'3. A galvanometer including a looped conductor adapted to receive current corresponding to vibrations to be measured, a reflector mounted on said conductor, a support for said conductor, an armature connected to said support, an electromagnetic means energized in'l accordance with the amplitude of said vibrations for moving said armature and thereby changing the position oi said support in accordance with the amplitude of said vibrations.

ERWIN GERLAC'JH. 

